The present invention relates to a wire cut electric discharge machine for machining a workpiece by generating electric discharge between the workpiece and a wire electrode traveling substantially vertically between upper and lower wire guide devices. More particularly, the present invention relates to a wire cut electric discharge machine having upper and lower wire guide devices between which a wire electrode is suspended and tensioned to move horizontally relative to the workpiece using linear motors.
Recently, sinker type electric discharge machines having a movable quill to which a tool electrode is attached and which use a linear motor to move the quill have been introduced. Use of a linear motor improves the response speed of a servo mechanism compared to the conventional combination of a rotation type servo motor and ball screw. As a result, the tool electrode moves rapidly in response to the state of a working gap formed between the tool electrode and the workpiece, enabling more stable electric discharge machining. In addition, this configuration contributes significantly to an improvement in the effects of a jump operation wherein dirty dielectric fluid entrapped in the work gap is periodically expelled as a result of rapid raising and lowering of the tool electrode, i.e., from the cavity being formed in the workpiece. As a result of the aforementioned jump operation and the high acceleration and deceleration capability of the linear motor, a deep cavity having a narrow opening can be formed in the workpiece in a shorter time and with higher precision. Also, because of the more effective jump operation, the operator is relieved of the highly skillful operation of ensuring precise flushing to maintain a continuous flow of dielectric fluid through the work gap in order to remove dirty dielectric fluid and supply fresh dielectric fluid.
Japanese laid-open patent No. 8-318433 discloses a wire electric discharge machine fitted with a linear motor. In this patent, a structure including work table having a work stand is provided on a lower saddle which is capable of movement in the direction of a horizontal Y axis. A lower saddle is provided on a bed capable of movement in the direction of the horizontal X axis which is orthogonal to the Y axis. A workpiece is mounted on the workstand, and a work tank that can store dielectric fluid is affixed on the work table. A wire electrode is vertically suspended under tension between upper and lower wire guide devices. The lower wire guide device is attached to a tip of a lower arm supported on a column. The upper wire guide device is attached to a lower end of a slider, and the slider is provided on a table which is movable in the vertical direction. The table is provided on a front surface of the upper saddle so as to be movable in the direction of a U axis which is parallel to the X axis. The upper saddle is provided on the column to be capable of movement in the direction of a V axis which is parallel to the Y axis. Movement mechanisms for the X, Y, U and V axes respectively have a built in linear motor.
An object of the present invention is to provide a wire cut electric discharge machine in which the inertial mass of a movable body that is moved by a linear motor is minimized.
Another object of the present invention is to provide a wire cut electric discharge machine capable of highly accurate positioning of upper and lower wire guide devices using a linear motor, without enlarging the size of the machine.
According to the present invention there is provided a wire electric discharge machine in which a wire electrode is suspended between upper and lower wire guide devices, the lower wire guide device being movable relative to the workpiece in a horizontal X-Y plane formed by orthogonal X and Y axes. The machine further comprises a stationary machine frame, a saddle provided on the machine frame, an X axis linear motor for moving the saddle in the X axis direction, a lower arm to which the lower wire guide device is attached, which extends in the direction of the Y axis. A ram, to which the lower arm is attached, is provided on the saddle, and has a Y axis linear motor for moving the ram in the Y axis direction. The X axis linear motor comprises a row of magnets fixed to the machine frame and an electromagnet fixed to a lower surface of the saddle, and the Y axis linear motor comprises an electromagnet fixed to an upper surface of the saddle and a row of magnets fixed to the ram.
Since the electromagnets for the linear motors have a shorter length than the row of magnets and are respectively fixed to the upper surface and lower surface of the saddle, the size and inertial mass of the saddle can be minimized.
Preferably, the centers of gravity of the electromagnet for the X axis linear motor and the electromagnet for the Y axis linear motor are aligned vertically.
Additional objects, advantages and novel features of the invention will be set forth in the description that follows, and in part will become apparent to those skilled in the art upon reading this description or practicing the invention. The objects and advantages of the invention may be realized and attained by practicing the invention as recited in the appended claims.